Semiconductor device and method for fabricating the same

ABSTRACT

A semiconductor device and a method of manufacturing the same. The semiconductor device includes a channel, a gate, and a memory layer is interposed between the channel and the gate. The memory layer includes a tunnel insulating layer adjacent to the channel, a charge blocking layer adjacent to the gate, and a charge storing layer interposed between the tunnel insulating layer and the charge blocking layer. The tunnel insulating layer includes a first insulating layer adjacent to the channel and an air layer interposed between the first insulating layer and the charge storing layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.14/159,226 filed on Jan. 20, 2014, which claims priority of KoreanPatent Application No. 10-2013-0129315, filed on Oct. 29, 2013. Thedisclosure of each of the foregoing application is incorporated hereinby reference in its entirety.

BACKGROUND

1. Field

Exemplary embodiments of the present invention relate to a semiconductordevice, and more particularly, to a semiconductor device including aplurality of memory cells stacked vertically from a substrate and amethod for fabricating the same.

2. Description of the Related Art

A NAND flash memory is an example of a memory device, which may storedata and maintain the stored data even though power supply is cut off.

Recently, the improvement in integration degree of a 2D semiconductordevice in which memory cells are formed as a single layer over a siliconsubstrate has reached the limit. Thus, there have been proposed avariety of 3D semiconductor devices in which a plurality of memory cellsare stacked vertically from a silicon substrate.

SUMMARY

Various embodiments are directed to a semiconductor device capable ofsecuring the operation characteristic and the data retentioncharacteristic of a memory cell and simplifying a fabrication process,and a method for fabricating the same.

In an embodiment, a semiconductor device may include a channel disposedover a substrate and extending in a direction substantiallyperpendicular to the substrate; a stacked structure comprising one ormore interlayer dielectric layers and one or more gates that arealternatively stacked over the substrate; and a memory layer interposedbetween the channel and the one or more gates, the memory layercomprising a tunnel insulating layer adjacent to the channel, a chargeblocking layer adjacent to the gate, and a charge storing layerinterposed between the tunnel insulating layer and the charge blockinglayer, wherein the tunnel insulating layer comprises a first insulatinglayer adjacent to the channel, and an air layer interposed between thefirst insulating layer and the charge storing layer.

In an embodiment, a semiconductor device may include a channel; a gate;and a memory layer interposed between the channel and the gate, thememory layer comprising a tunnel insulating layer adjacent to thechannel, a charge blocking layer adjacent to the gate, and a chargestoring layer interposed between the tunnel insulating layer and thecharge blocking layer, wherein the tunnel insulating layer comprises afirst insulating layer adjacent to the channel and an air layerinterposed between the first insulating layer and the charge storinglayer.

In an embodiment, a method for fabricating a semiconductor device mayinclude: forming a stacked structure over a substrate, the stackedstructure including a plurality of interlayer dielectric layers and aplurality of material layers, which are alternately stacked; selectivelyetching the stacked structure to form a first channel hole through thestacked structure; sequentially forming a charge blocking layer, acharge storing layer, a second sacrificial layer, and a first insulatinglayer on a sidewall defining the first channel hole; forming an airlayer by removing the second sacrificial layer; and forming a channel inthe first channel hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F are cross-sectional views showing a semiconductor deviceand a method of fabricating the same in accordance with an embodiment ofthe present invention.

FIG. 2 is a diagram illustrating an energy band of a memory cell inaccordance with the embodiment of the present invention and an energyband of a memory cell in accordance with a first comparative example.

FIG. 3 is a diagram illustrating the energy band of the memory cell inaccordance with the embodiment of the present invention and an energyband of a memory cell in accordance with a second comparative example.

FIG. 4 is a diagram illustrating the energy band of the memory cell inaccordance with the embodiment of the present invention and an energyband of a memory cell in accordance with a third comparative example.

FIGS. 5A to 5E are cross-sectional views showing semiconductor deviceand a method of fabricating the same in accordance with anotherembodiment of the present invention.

FIG. 6 is a cross-sectional view showing a semiconductor device inaccordance with another embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a semiconductor device and amethod for fabricating the same in accordance with an embodiment of thepresent invention.

FIGS. 8A to 9 are diagrams showing a semiconductor device and a methodfor fabricating the same in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

Various embodiments will be described below in more detail withreference to the accompanying drawings. The present invention may,however, be embodied in different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the present invention to those skilled inthe art. Throughout the disclosure, reference numerals corresponddirectly to the like numbered parts in the various figures andembodiments of the present invention.

The drawings are not necessarily to scale and in some instances,proportions may have been exaggerated in order to clearly illustratefeatures of the embodiments. It should be readily understood that themeaning of “on” and “over” in the present disclosure should beinterpreted in the broadest manner such that “on” means not only“directly on” but also “on” something with an intermediate feature(s) ora layer(s) therebetween, and that “over” means not only directly on topbut also on top of something with an intermediate feature(s) or alayer(s) therebetween.

FIGS. 1A to 1F are cross-sectional views showing a semiconductor deviceand a method for fabricating the same accordance with an embodiment ofthe present invention.

First, the fabrication method will be described.

Referring to FIG. 1A, a plurality of interlayer dielectric layers 110and a plurality of first sacrificial layers 120 may be alternatelystacked over a substrate 100 in which required predetermined structures,for example, a source region and the like may be formed.

The first sacrificial layer 120 is a layer to be replaced with aconductive layer that is used as a gate of a memory cell during asubsequent process, and may be formed of a layer having a different etchrate from the interlayer dielectric layer 110, for example, an oxidelayer. The interlayer dielectric layer 110 serves to insulate gates ofmemory cells, positioned at the top and bottom thereof, from each otherand may be formed of an oxide layer, for example.

FIG. 1A illustrates four first sacrificial layers 120, but the presentinvention is not limited thereto. One or more first sacrificial layers120 may be stacked, and the number of first sacrificial layers may beset based on desired characteristics.

The stacked structure of the interlayer dielectric layers 110 and thefirst sacrificial layers 120 may be selectively etched to form a channelhole H that exposes the substrate 100 through the stacked structure. Thechannel hole H may be formed to expose a source region that is formed inthe substrate 100 and not illustrated in FIG. 1A.

Referring to FIG. 13, a charge blocking layer 132, a charge storinglayer 134, a second sacrificial layer 136, and a first insulating layer138 may be sequentially formed on the sidewall of the channel hole H.

The charge blocking layer 132 serves to block the transfer of chargebetween the gate of the memory cell and the charge storing layer 134,and may be formed of an oxide layer, for example, a silicon oxide layer.The charge storing layer 134 serves to store charges therein, and may beformed of a nitride layer capable of trapping charges, for example, asilicon nitride layer. The second sacrificial layer 136 is a layer thatis removed to be air during a subsequent process, and may be formed of alayer that has a different etch rate from the charge blocking layer 132,the charge storing layer 134, and the first insulating layer 138. Thesecond sacrificial layer 136 may be, for example, a carbon layer. Thefirst insulating layer 138 may function as a tunnel insulating layerwith air, and may be formed of an oxide layer, for example, a siliconoxide layer. The tunnel insulating layer may serve as a layer fortunneling charge between a channel and the charge storing layer 134.

The charge blocking layer 132, the charge storing layer 134, the secondsacrificial layer 136, and the first insulating layer 138 may be formedby sequentially depositing an oxide layer, a nitride layer, a carbonlayer, and an oxide layer on the resultant structure of FIG. 1A andperforming a blanket etching process to expose the substrate 100 and theuppermost interlayer dielectric layer 110.

Alternatively, the charge blocking layer 132, the charge storing layer134, the second sacrificial layer 136, and the first insulating layer138 may be formed by sequentially performing a deposition process and ablanket etching process for an oxide layer, a deposition process and ablanket etching process for a nitride layer, a deposition process and ablanket etching process for a carbon layer, and a deposition process anda blanket etching process for an oxide.

Referring to FIG. 1C, the second sacrificial layer 136 may be removed.Thus, the space may be formed by removing the second sacrificial layer136. That is, the second sacrificial layer 136 may be the air layer A.

If the second sacrificial layer 136 is formed of a carbon layer, thenthe removal of the second sacrificial layer 136 may be performed usingoxygen-containing plasma. If the oxygen-containing plasma, for example,O₂ plasma is implanted into the resultant structure of FIG. 1B, carbonof the second sacrificial layer 136 may react with oxygen and thenescape as CO_(x) gas. The CO_(x) gas may escape through the opened topsurface of the second sacrificial layer 136. Furthermore, if the firstinsulating layer 138 is formed of an oxide layer, which is not dense,the CO_(x) gas may escape through the first insulating layer 138.

As the result of this process, a memory layer 130, in which the chargeblocking layer 132, the charge storing layer 134, the air layer A, andthe first insulating layer 138 are sequentially disposed, may be formedon the sidewall of the channel hole H. As described above, the air layerA and the first insulating layer 138 may function as a tunnel insulatinglayer in the memory layer 130.

Referring to FIG. 1D, a semiconductor material, for example, polysiliconor the like, may be buried in the channel hole H having the memory layer130 formed therein, thereby forming a channel 150. The channel 150 mayhave a pillar shape extending in a direction substantially perpendicularto the substrate 100. Furthermore, the channel 150 may be electricallycoupled to the source region formed in the substrate 100.

The channel 150 may be formed by the following process by depositing asemiconductor material over the resultant structure of FIG. 1C to such athickness as to sufficiently fill the channel hole H. The depositedsemiconductor material is planarized, by, for example a chemicalmechanical polishing (CMP) process, to expose the uppermost interlayerdielectric layer 110.

During the above-described channel formation process, the air layer Amay be maintained. Since the air layer A has a very small width in adirection parallel to the substrate 100, the top of the air layer A maybe blocked by the semiconductor material at the initial stage of theprocess of depositing the semiconductor material. Thus, at least the airlayer A between the first sacrificial layer 120 and the channel 150 maybe maintained. In particular, when the channel 150 is formed of a layerhaving a poor step coverage characteristic, the air layer A may bemaintained more reliably.

Referring to FIG. 1E, the stacked structure of the interlayer dielectriclayer 110 and the first sacrificial layer 120 may be selectively etchedto form a slit S in the stacked structure. The slit S may be formed tosuch a depth as to pass through at least the lowermost first sacrificiallayer 120. Furthermore, the slit S may have various shapes. For example,the slit. S may have a line shape extended in a direction perpendicularto the cross-section of FIG. 1E, but the present invention is notlimited thereto. The slit S may include any shape that may expose all ofthe first sacrificial layers 120.

The first sacrificial layer 120, exposed through the slit S, may beremoved. A space created by removing the first sacrificial layers 120may be referred to as a groove G. The removal of the first sacrificiallayer 120 may be performed through a wet or dry etching process. Whenthe first sacrificial layer 120 is removed, the top to surfaces of thechannel layer 150 and the memory layer 130 may be may be covered andprotected by a protective layer (not illustrated).

Referring to FIG. 1F, the groove G may be filled with a conductivematerial to form a gate 160 of a memory cell. The gate 160 may be formedof various conductive materials including: metal, metal nitride,polysilicon doped with an impurity or a combination thereof.

Although not illustrated, a required subsequent process, for example, aprocess for forming a bit line coupled to the top of the channel 150 maybe performed,

Through the above-described process, the exemplary semiconductor device,as illustrated in FIG. 1F, may be fabricated.

Referring to FIG. 1F, the semiconductor device in accordance with theembodiment of the present invention may include the channel 150extending in a direction substantially perpendicular to the substrate100, the stacked structure in which the plurality of interlayerdielectric layers 110 and a plurality of gates 160 are alternatelystacked over the substrate 100, and the memory layer 130 interposedbetween the stacked structure and the channel 150. Thus, the memorylayer 130 may have a pillar shape extending in the directionsubstantially perpendicular to the substrate. When seen from the top,the memory layer 130 may have a shape to surround the channel 150.

In the present embodiment, the memory layer 130 may include the chargeblocking layer 132, the charge storing layer 134, the air layer A, andthe first insulating layer 138, which are sequentially disposed from theside closest to the stacked structure.

One channel 150, one gate 160 contacted with the channel 150 with thememory layer 130 interposed therebetween, and the memory layer 130 mayform one memory cell. Depending on whether charges are injected into thecharge storing layer 134 of the memory layer 130 from the channel 150 ordischarged from the charge storing layer 134 according to a voltageapplied to the gate 160 of the memory cell, data may be stored in thememory cell or erased from the memory cell such that the memory cell hasa different state.

More specifically, an erase operation for erasing data of a memory cellmay be performed by a method of tunneling and injecting holes into thecharge storing layer 134 from the channel 150 and/or a de-trap method ofde-trapping electrons of the charge storing layer 134 to the channel150. A program operation for storing data into a memory cell may beperformed by transferring electrons/holes in the opposite direction ofthe erase operation. In particular, the program operation may beperformed by an incremental step pulse program (ISPP) method in which anincremental program voltage is applied to the gate 160 so as to inject asmall amount of electrons at a time.

The effect that may be obtained when the air layer A and the firstinsulating layer 138 are used as the tunnel insulating layer will bedescribed below with reference to FIGS. 2 to 4.

In the present embodiment, it has been described that the memory layer130 has a shape that extends along the sidewall of the channel 150 inthe direction perpendicular to the substrate 100, but the presentinvention is not limited thereto. The memory layer 130 may be formed invarious shapes, as long as the memory layer 130 is interposed betweenthe gate 160 and the channel 150.

Furthermore, it has been described that the first sacrificial layer 120is replaced with the gate 160, but the present invention is not limitedthereto. In another embodiment, a conductive layer may be directlydeposited instead of the first sacrificial layer 120. That is, duringthe process of FIG. 1A, the first sacrificial layer 120 may be replacedwith a conductive layer. In this case, the processes of FIGS. 1E and 1Fmay be omitted.

FIG. 2 is a diagram illustrating an energy band of the memory cell inaccordance with the embodiment of the present invention and an energyband of a memory cell in accordance with a first comparative example.The energy band of the memory cell in accordance with the embodiment ofthe present invention is indicated by a thin solid line. The energy bandof the memory cell in accordance with the first comparative example isindicated by a dotted line, and an overlapping portion therebetween isindicated by a thick solid line. Furthermore, in FIG. 2, the gate, thecharge blocking layer, the charge storing layer, the tunnel insulatinglayer, and the channel of each memory cell are represented by Gate, Box,CTN, Tox, and CH, respectively.

FIG. 2 illustrates a case in which the memory cell in accordance withthe exemplary implementation of the present invention uses an oxidelayer as the charge blocking layer Box, a nitride layer as the chargestoring layer CTN, and an air layer and an oxide layer as the tunnelinsulating layer Tox. In contrast, the memory cell in accordance withthe first comparative example uses only an oxide layer having the samethickness, as the tunnel insulating layer Tox. In other words, thethickness of the tunnel insulating layer Tox in accordance with thepresent embodiment, that is, the sum of the air layer and the oxidelayer is equal to the thickness of the tunnel insulating layer Tox ofthe memory cell in accordance with the first comparative example, thatis, the thickness of the oxide layer. At this time, the thickness mayindicate a width in a direction parallel to the substrate 100 in FIGS.1A to 1F.

Furthermore, the thickness of the tunnel insulating layer Tox inaccordance with the present embodiment may be set to such a thicknessthat direct tunneling of charges does not occur, for example, about 20 Åor more. If the thickness of the tunnel insulating layer Tox is so smallthat direct tunneling of charges occurs, then a program operation basedon the ISPP method cannot be performed, and a data retentioncharacteristic of the memory cell may be degraded. Thus, the thicknessesof the air layer and the oxide layer in the tunnel insulating layer Toxin accordance with the present embodiment may be suitably adjusted. Forexample, the thickness of the air may be set to about 10 Å, and thethickness of the oxide layer may be set to about 25 Å.

Referring to FIG. 2, it can be seen that, during the erase operation, atunnel barrier width {circle around (1)} from the channel CH to thecharge storing layer CTN in the memory cell in accordance with thepresent exemplary embodiment is smaller than a tunnel barrier width{circle around (2)} from the channel CH to the charge storing layer CTNin the memory cell in accordance with the first comparative example.

Thus, in the memory cell in accordance with the present embodiment, alarge amount of holes h may be injected into the charge storing layerCTN within a short time, compared to the memory cell in accordance withthe first comparative example. Thus, the erase speed may besignificantly improved.

FIG. 3 is a diagram illustrating the energy band of the memory cell inaccordance with the embodiment of the present invention and an energyband of a memory cell in accordance with a second comparative example.The energy band of the memory cell in accordance with the presentembodiment is indicated by a thin solid line, the energy band of thememory cell in accordance with the second comparative example isindicated by a dotted line, and an overlapping portion therebetween isindicated by a thick solid line.

Referring to FIG. 3, the memory cell in accordance with the presentembodiment is substantially the same as described with reference to FIG.2. In contrast, the memory cell in accordance with the secondcomparative example uses an air layer having the same thickness, as thetunnel insulating layer Tox. In other words, the thickness of the tunnelinsulating layer Tox in accordance with the present embodiment, that is,the sum of the air layer and the oxide layer may correspond to such athickness that direct tunneling of charges does not occur, and may besubstantially equal to the thickness of the tunnel insulating layer Toxin the memory cell in accordance with the second comparative example,that is, the thickness of the air layer.

Referring to FIG. 3, it can be seen that, during the erase operation,the de-trap efficiency of electrons in the memory cell in accordancewith the second comparative example (refer to) is lower than the de-trapefficiency of electrons in the memory cell in accordance with thepresent exemplary implementation (refer to {circle around (3)}).However, the erase operation in the memory cell in accordance with thesecond comparative example may be performed only through electronde-trap. As described above, the thickness of the air layer serving asthe tunnel insulating layer Tox of the memory cell in accordance withthe second comparative example corresponds to such a thickness thatdirect tunneling of charges does not occur, and hole injection caused bytunneling of holes does not occur because the air has no valance band.

Thus, the memory cell in accordance with the second comparative examplehas lower erase speed than the memory cell in accordance with thepresent embodiment.

FIG. 4 is a diagram illustrating the energy band of the memory cell inaccordance with the embodiment of the present invention and an energyband of a memory cell in accordance with a third comparative example.The energy band of the memory cell in accordance with the presentembodiment is indicated by a thin solid line, the energy band of thememory cell in accordance with the third comparative example isindicated by a dotted line, and an overlapping portion therebetween isindicated by a thick solid line.

Referring to FIG. 4, the memory cell in accordance with the presentembodiment may be substantially the same as described with reference toFIG. 2. In contrast, the memory cell in accordance with the thirdcomparative example uses only an air layer as the tunnel insulatinglayer Tox. In particular, in order to secure the same erase speed as thememory cell in accordance with the present embodiment, the tunnelinsulating layer Tox of the memory cell in accordance with the thirdcomparative example may have a smaller thickness than the tunnelinsulating layer Tox of the memory cell in accordance with the presentembodiment. For example, if the air layer and the oxide layer formingthe tunnel insulating layer Tox in the memory cell in accordance withthe present embodiment have a thickness of about 10 Å and 25 Å,respectively, then the thickness of the air layer, at which the memorycell in accordance with the third comparative example may secure thesame erase speed, may correspond to about 17 Å.

When the thickness of the tunnel insulating layer Tox in the memory cellin accordance with the third comparative example is reduced, the erasespeed may be improved. This is because the de-trap efficiency ofelectrons may be increased and direct tunneling of holes h may occur(refer to {circle around (5)}). In this case, however, the degradationof data retention characteristic inevitably occurs and the programoperation based on the ISPP method may not be performed.

Thus, the memory cell in accordance with the present embodiment may havean excellent data retention characteristic and perform a programoperation based on the ISPP method, compared to the memory cell inaccordance with the third comparative example.

In short, when a double layer of air and oxide is used as the tunnelinsulating layer like the memory cell in accordance with the presentembodiment, the erase speed may be increased more than when a monolayerof oxide or air having the same thickness is used. Furthermore, when thesame erase speed as the monolayer layer of oxide or air is used as thetunnel insulating layer may be secured, the thickness of the tunnelinsulating layer may be increased more than the monolayer layer of oxideor air. Thus, the data retention characteristic may be secured, and theprogram operation based on the ISPP method may be performed,

FIGS. 5A to 5E are cross-sectional views showing a semiconductor deviceand a method of fabricating the same in accordance with anotherembodiment of the present invention. The following descriptions will befocused on differences from the above-described embodiment.

Referring to FIG. 5A, a conductive layer 202 having one or more thirdsacrificial layers 204 buried therein may be formed over a substrate 200in which required predetermined lower structures, for example, anuppermost insulating layer and the like may be formed.

The third sacrificial layer 204 serves to provide a space in which apair of channels (to be described below) are coupled to each other, andmay be formed of various materials that have a different etch rate fromthe interlayer dielectric layer 210 and the first sacrificial layer 220and that may be easily removed.

The third sacrificial layer 204 may have an island shape when seen fromthe top. Although not illustrated, a plurality of third sacrificiallayers 204 may be arranged in the cross-sectional direction of FIG. 5Aand a direction crossing the cross-sectional direction.

The conductive layer 202 may be formed of various conductive materialsincluding a metal, a metal oxide, polysilicon doped with an impurity, ora combination thereof. In the present embodiment, the conductive layer202 may have a plate shape when seen from the top, and may be formed tosurround the side and bottom of the third sacrificial layer 204.However, the present invention is not limited thereto. The conductivelayer 202 may include any additional structures so long as theconductive layer 202 is contacted with at least a part of the thirdsacrificial layer 204. Alternatively, the conductive layer 202 may beomitted.

A plurality of interlayer dielectric layers 210 and a plurality of firstsacrificial layers 220 may be alternately stacked over the thirdsacrificial layer 204 and the conductive layer 202.

Referring to FIG. 5B the stacked structure of the interlayer dielectriclayers 210 and the first sacrificial layers 220 may be selectivelyetched to form a pair of first channel holes H1 that expose the thirdsacrificial layer 204 through the stacked structure. The first channelholes H1 may extend in a direction substantially perpendicular to thesubstrate 100.

As the third sacrificial layer 204, which is exposed by the firstchannel hole H1, is removed through a wet etching process or the like, asecond channel hole H2, corresponding to the space formed by the removalof the third sacrificial layer 204, may be formed. The second channelhole H2 may serve to couple the pair of first channel holes H1 at thebottom of the first channel holes H1. Through this process, a U-shapedchannel hole may be formed (refer to H1 and H2).

Referring to FIG. 5C, a charge blocking layer 232, a charge storinglayer 234, a second sacrificial layer 236, and a first insulating layer238 may be sequentially formed along the inner walls of the first andsecond channel holes H1 and H2.

The charge blocking layer 232, the charge storing layer 234, the secondsacrificial layer 236, and the first insulating layer 238 may be formedby sequentially depositing an oxide layer, a nitride layer, a carbonlayer, and an oxide layer over the resultant structure of FIG. 5B andperforming a planarization process, for example, a CMP process, toexpose the uppermost interlayer dielectric layer 210.

Referring to FIG. 5D, a part of the second sacrificial layer 236 may beremoved to be an air layer A. The second sacrificial layer 236 of whichthe part is removed will be hereafter referred to as a secondsacrificial layer pattern 236A.

The second sacrificial layer pattern 236A may be not completely removedsuch that the second sacrificial layer pattern 236A is positioned underat least the bottom of the lowermost first sacrificial layer 220. If thesecond sacrificial layer 236 is a carbon layer, then a plasma injectiontime during which oxygen-containing plasma is injected may be adjustedsuch that at least a part of the second sacrificial layer 236 is leftwhile the top of the second sacrificial layer pattern 236A is set to alower level than the bottom of the lowermost first sacrificial layer220.

Thus, a memory layer 230, in which the charge blocking layer 232, thecharge storing layer 234, the air layer A, and the first insulatinglayer 238 are sequentially disposed, may be formed between the firstsacrificial layer 220 and the channel. The air layer A and the firstinsulating layer 238 may function as a tunnel insulating layer in thememory layer 230. The second sacrificial layer 236A may contact thelower part of the charge storing layer 234 and the lower part of thefirst insulating layer 238 in a region where the first sacrificial layer220 does not exist. For example, a region where the second sacrificiallayer 236A contacts the conductive layer 202, thereby supporting thefirst insulating layer 238 and maintaining the air layer A.

Referring to FIG. 5E, a semiconductor material is buried in the firstand second channel holes H1 and H2, which have the memory layer 230formed therein, thereby forming a channel 250. The channel 250 mayinclude a pair of pillar parts extending in a direction substantiallyperpendicular to the substrate 200 and may include a coupling part tocouple the pair of pillar parts at the bottom of the pair of pillarparts. Thus, the channel 250 may have a U-shape.

Although not illustrated, a process similar to that described withreference to FIGS. 1E and 1F may be performed to replace the firstsacrificial layer 220 with a gate. In this case, a plurality of memorycells each including the gate, the charge blocking layer 232, the chargestoring layer 234, the air layer A, the first insulating layer 238, andthe channel 250 may be formed as illustrated in FIG. 1F. The pluralityof memory cells may be stacked over the substrate 100. Under theplurality of memory cells, a pipe transistor to control the couplingbetween the pair of pillar parts of the channel 250 may be disposed. Thepipe transistor may include the conductive layer 202 serving as thegate, the coupling part of the channel 250, and the gate dielectriclayer interposed therebetween and including the charge blocking layer232, the charge storing layer 234, the air layer A or the secondsacrificial layer pattern 236A, and the first insulating layer 238.

Although not illustrated, required subsequent processes, for example, aprocess of forming a bit line to be coupled to any one of the tops ofthe pair of pillar parts of the channel 250 and a process of forming asource line to be coupled to the other one of the tops of the pair ofpillar parts of the channel 250 may be additionally performed,

The semiconductor device in accordance with the present embodiment issimilar to the above-described embodiment, except that the U-shapedmemory string is formed. Thus, the semiconductor device may secure thesame as or similar effect to the above-described embodiment.

In the above-described embodiments, it has been described that thechannel fills the entire portion of the channel hole having the memorylayer formed therein. However, the present invention is not limitedthereto. In an alternative implementation, the channel may fill only apart of the channel hole. This will be described below with reference toFIG. 6.

FIG. 6 is a cross-sectional view showing a semiconductor device inaccordance with another embodiment of the present invention.

Referring to FIG. 6, a channel 250′ in accordance with the presentembodiment may be formed on the memory layer 230 to such a thicknessthat the channel holes having the memory layer 230 formed therein (referto H1 and H2 of FIG. 5B) are not completely filled. The other space ofthe channel hole having the memory layer 230 and the channel 250′ formedtherein may be filled with an insulating layer 260, such as an oxidelayer or a nitride layer.

With respect to FIGS. 5A to 5E, it has been described that a part of thesecond sacrificial layer 236 is left to support the first insulatinglayer 238 and maintain the air layer A. However, the present inventionis not limited thereto. For example, in an alternative implementation,the support layer for the first insulating layer 238 and the air layer Amay be formed in various shapes through various methods. This will bedescribed below with reference to FIGS. 7 to 9.

FIG. 7 is a cross-sectional view showing a semiconductor device and amethod of fabricating the same in accordance with another embodiment ofthe present invention.

First, the processes of FIGS. 5A to 5C are performed.

Referring to FIG. 7, a thermal oxidation process may be performed on theresultant structure of FIG. 5C, and the entire part of the secondsacrificial layer 236 may be removed to form an air layer A. In thiscase, the second sacrificial layer 236 may be formed of a material thatis heated and removed, such as a carbon layer.

During the thermal oxidation process, a bias power may be applied fromupward to downward in a direction substantially perpendicular to thesubstrate 200 (refer to the arrow of FIG. 7). If the first insulatinglayer 238 is formed of an oxide layer that is not dense, then anoxidation gas may pass through the first insulating layer 238 in aregion corresponding to the first channel hole extending in the verticaldirection (refer to H1 of FIG. 5B), and then oxidize at least a part ofthe charge storing layer 234. If the charge storing layer 234 is formedof a layer of which the volume is expanded during oxidation (forexample, a nitride layer), then an oxide layer of a material forming thecharge storing layer 234 (for example, oxynitride) may be buried betweenthe first insulating layer 238 and the charge storing layer 234 duringthis oxidation process. The oxide layer of the material forming thecharge storing layer 234 maybe contacted with the charge storing layer234 and the first insulating layer 238 in the region corresponding tothe first channel hole, thereby supporting the first insulating layer238 and the air layer A. Thus, the oxide layer is referred to as asupport layer 270.

FIG. 7 illustrates a case in which a part of the charge storing layer234 is oxidized in the region corresponding to the first channel hole,but the present embodiment is not limited thereto. For example, in analternative implementation, the entire charge storing layer 234 may beoxidized in the corresponding region. In this case, the bottom of thesupport layer 270 may be contacted with the charge blocking layer 232 inthe corresponding region.

Since a channel formation process and a gate formation process that maybe subsequently performed are substantially the same as described above,the detailed descriptions thereof are omitted herein.

FIGS. 8A to 9 are diagrams showing a semiconductor device and a methodof fabricating the same in accordance with another embodiment of thepresent invention. In particular, FIGS. 8A and 9 are cross-sectionalviews, and FIG. 88 is a plan view based on one first channel hole ofFIG. 8A.

First, the processes of FIGS. 5A to 5C are performed.

Referring to FIGS. 8A and 88, a channel 250 may be formed in the channelholes (refer to H1 and H2 of FIG. 5B), and a support layer 280 may beformed over the resultant structure. The support layer 280 may be formedof an insulating material such as oxide or nitride.

The support layer 280 may be contacted with the top surfaces of thecharge blocking layer 232, the charge storing layer 234, the secondsacrificial layer 236, the first insulating layer 238, the channel 250,and the uppermost interlayer dielectric layer 210 across the firstchannel hole H1, when seen from the top. At this time, the support layer280 may have a width that does not completely cover the first channelhole, and may expose at least a part of the top surface of the secondsacrificial layer 236.

Referring to FIG. 9, the entire part of the second sacrificial layer 236exposed by the support layer 280 may be removed through oxygen plasma orthe like, to form an air layer A. Although the entire part of the secondsacrificial layer 236 is removed, the support layer 280 may be contactedwith the top surface of the first insulating layer 238 so as to supportthe first insulting layer 238. Thus, the air layer A between the firstinsulating layer 238 and the charge storing Mayer 234 may be maintained.

Since a subsequent gate formation process is substantially the same asdescribed above, the detailed descriptions thereof are omitted herein.

In accordance with the embodiments of the present invention, it ispossible to secure the operation characteristic and the data retentioncharacteristic of the memory cell and simplify the fabrication process.

Although various embodiments have been described for illustrativepurposes, it will be apparent to those skilled in the art that variouschanges and modifications may be made without departing from the spiritand scope of the invention as defined in the following claims.

What is claimed is:
 1. A method of fabricating a semiconductor device,the method comprising: forming a stacked structure over a substrate, thestacked structure including a plurality of interlayer dielectric layersand a plurality of material layers, which are alternately stacked;selectively etching the stacked structure to form a first channel holethrough the stacked structure; sequentially forming a charge blockinglayer, a charge storing layer, a second sacrificial layer, and a firstinsulating layer on a sidewall defining the first channel hole; formingan air layer by removing the second sacrificial layer; and forming achannel in the first channel hole.
 2. The method of claim 1, wherein theforming the second sacrificial layer and the forming a first insulatinglayer comprises: forming the second sacrificial layer and the firstinsulating layer to a thickness that prevents direct tunneling of acharge.
 3. The method of claim 1, wherein the second sacrificial layeris formed of carbon.
 4. The method of claim 3, wherein the forming anair layer comprises: removing the second sacrificial layer using anoxygen-containing plasma.
 5. The method of claim 1, wherein the firstchannel hole include a pair of first channel holes, and the methodfurther comprising, before the forming the stacked structure: forming asecond conductive layer on the substrate; and forming a thirdsacrificial layer in the second conductive layer; and the method furthercomprising, after the forming the first channel hole: forming a secondchannel hole by removing the third sacrificial layer which is exposed bythe pair of first channel holes.
 6. The method of claim 5, wherein thecharge blocking layer, the charge storing layer, the second sacrificiallayer, and the first insulating layer are sequentially formed on aninner wall of the second channel hole.
 7. The method of claim 6, whereinthe forming an air layer further comprises: not removing at least a partof the second sacrificial layer facing the second conductive layer. 8.The method of claim 6, wherein the second sacrificial layer is formed ofa material that is removed by heat, the charge storing layer is formedof a material that undergoes a volume increase when oxidized, and theforming an air layer comprises: thermally oxidizing the secondsacrificial layer in a state where a bias power is applied from upwardto downward to remove the second sacrificial layer.
 9. The method ofclaim 6, further comprising: forming, over the stacked structure, asupport layer crossing the first channel hole and exposing a part of thetop surface of the second sacrificial layer, before the forming an airlayer.